Corona discharge device

ABSTRACT

Corona discharge equipment for poorly conducting material is characterised in that one of a pair of electrodes is a rigidly mounted conductor having discrete discharge points spaced therealong while the other electrode of the pair is a resiliently supported conductor, the resilient support of which ensures the maintenance of a substantially constant distance between the electrodes of the pair and between the other electrode and the surface to be treated.

United States Patent [191 Spengler [451 Aug. 20, 1974 CORONA DISCHARGE DEVICE Inventor: Walter Spengler, Stehlgasse, CH

4105 Biel-Benken, Switzerland Filed: May 22, 1973 Appl. No.: 362,939

Foreign Application Priority Data June 15, 1972 Switzerland 8966/72 US. Cl 317/2 F, 317/4 Int. Cl H01t 19/00, H05f 3/06 Field of Search 317/2 F, 4 1

References Cited UNITED STATES PATENTS 7/1969 Del Vecchio et al 317/4 3,566,223 2/1971 Salger 317/4 Primary Examiner-L. T. l-lix Attorney, Agent, or FirmWenderoth, Lind & Ponack [5 7] ABSTRACT Corona discharge equipment for poorly conducting material is characterised in that one of a pair of electrodes is a rigidly mounted conductor having discrete discharge points spaced therealong while the other electrode of the pair is a resiliently supported conductor, the resilient support of which ensures the maintenance of a substantially constant distance between the electrodes of the pair and between the other electrode and the surface to be treated.

4 Claims, 6 Drawing Figures CORONA DISCHARGE DEVICE BACKGROUND OF THE INVENTION The invention relates to equipment for discharging an electrostatic potential from the surface of a material that is a poor conductor of electricity by corona discharge. As such, equipment of this kind is well known.

conductor is provided with corona discharge points and.

earthed, whereas the higher potential conductor is connectable to a source of high voltage. In part, to eliminate any risk of deposits on the conductors creating an increased tendency to short circuiting between the electrodes and in part to preclude any contact with the high voltage conductor or conductors, the latter, in a known arrangement, is or are embedded in a body of electrically insulating material.

It is a defect of those known types of equipment that the insulating bodies, which for reasons of economy are fairly flat, have a tendency to warp longitudinally and transversely when subjected to temperature stress. This circumstance limits their possible length.

SUMMARY OF THE INVENTION It is an object of the present invention to provide equipment of the specified kind which can be built to any desired length economically, without risk of warping, and without incurring the penalty of losing some of the advantages of conventional devices of this kind.

According to the present invention equipment for discharging an electrostatic potential from a surface of a material that is a poor conductor of electricity by passing the material through an electric corona discharge generated between a pair of electrodes extending between lateral bearing members is characterised in that one of the pair is a rigid conductor having discrete discharge points spaced therealong which is rigidly fixed between the bearing members and in that the other electrode of the pair is a conductor supported in the bearing member by resilient means allowing relative movement of such other electrode with one of the bearing means, to ensure the maintenance of a substantially constant distance between the electrodes of the pair and between such other electrode and the surface of the material to be treated.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of equipment in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is an end elevation of one embodiment of equipment according to the invention for the treatment of sheet materials, such as paper and textile webs, seen in the direction of travel of the treated material,

FIG. 2 is a plan from above of part of the equipment according to FIG. 1,

FIG. 3 is a cross sectional representation of a second embodiment of equipment according to the invention for treating the exterior surface of a bar or tube stock,

FIGS. 4 and 5 are structural details relating to the fixing of conductor elements to lateral holders in equipment according to FIG. 3, although the same principle could be applied to other embodiments of the invention, and

FIG. 6 is an illustration of part of a third embodiment of equipment in accordance with the invention for the treatment of tube sections or materials that have been formed into a sheath, or for the treatment of a web of material at a point where the proposed equipment is adapted to form a deflection or transport direction modifying device.

DETAILED DESCRIPTION OF THE INVENTION With reference to FIGS. 1 and 2, a frame structure 1, which in the illustrated embodiment has the shape of a U-section channel, comprises a bottom plate 1, which serves as a base and as a mounting plate, and flanges 2, 2 forming bearing supports into which a plurality of first bar-shaped electrodes 4, each provided with spaced-apart points 3, is inserted and which also carry a plurality of second electrodes 5. In order to prevent distortion, due to expansion of the electrodes 4 in the frame structure, the electrodes 4 are preferably fixed to the frame structure only at one end, as can be seen on the left in FIGS. 1 and 2. In a modified embodiment in which the bottom plate 1' is dispensed with, the electrodes 4 are preferably firmly fixed to the bearing support 2, 2 at each end and thus help to define a relatively rigid self-supporting frame.

During the use of the equipment shown in FIGS. 1 and 2, the first electrodes 4 are all connected to earth potential (i.e., if the bearing supports 2, 2' are of metal, the electrodes 4 are electrically connected to them. The second electrodes 5 are electrically insulated from the supports 2, 2' but are electrically connected to a high voltage source (not shown in the drawing) of which one terminal is earthed (and thus effectively electrically connected to the first electrodes 4) whereas the other terminal is connected to the second electrodes.

In order to ensure that each electrical conductor length forming a second electrode 5 always remains tightly stretched between the bearing holders 2 and 2 irrespective of temperature fluctuations (so that the distances from the points 3 of the first electrodes and from the surface of the material being treated will always remain the same) it is preferred to provide at least at one end of each electrode 5, a bearing element in the bearing holder 2 or 2 which is capable of compensating for thermal expanison. FIGS. 1 and 2 show for this purpose, compression springs 6 one end of each of which bears against a washer 7 on the outside of the bearing holders 2, 2' and the other end of each of which bears against a spring retainer 8 fixed to the electrode 5. The washer 7, and conveniently also the spring retainer 8, will consist of electrically insulating material when the bearing holders 2, 2 are of metal construction. The electrode 5 may be provided with an electrically insulating coating and this is shown protected, in the vicinity of the bearing holdings, by the provision of an insulating sleeve 9 surrounding the electrode in its passage through the holders. The spring retainer 8 is conveniently so connected to the conducting insulation that in the event of a fracture of or damage to one of the electrodes 5 only the affected conductor section need be repaired.

As illustrated, the electrodes 5 are defined by lengths of a single conductor forming a succession of hairpins which comprise a substantial proportion or all the electrodes in the equipment. Alternatively, the electrodes 5 may be separate conductor elements which are surface insulated in the zones confronting the electrodes 4, and which are electrically connected together in series, one or both ends of the resultant line of conductors being connected to the high voltage terminal of the high voltage source.

It will be readily understood that equipment of the kind illustrated in FIGS. 1 and 2 can be designed to substantially any desired width to fit any machine or installation that is to be provided with the equipment. It is not essential that the holders 2, 2' should form an unbroken line from one end to'the other of the equipment, since the lengths of neighbouring electrodes may be designed to be of different lengths. The bottom plate 1' in the illustrated frame 1 may be dispensed with if the machine or plant to which the equipment is tobe fitted already has elements capable of performing the functions of a bottom plate, i.e., to secure and locate the bearing holders 2, 2'.

In the event of the equipment being required to be so wide that the maintenance of reliable parallelism of the electrodes 4 and 5 ceases to be certain, intermediate support means of an electrically insulating material (insulating at least in regions adjacent to the electrodes 4, 5) may be provided and affixed to the bottom plate 1, if this is present, or otherwise to a suitable part of the machine or plant.

FIG. 3 is a cross section of second embodiment of equipment which is suitable for the treatment of bar or tube stock. In FIG. 3 there is provided an annular bearing flange 21 which has a centre opening 22 suitable for the passage therethrough of a cylindrical workpiece 23. The flange 21 which is associated at the other end of the equipment with a flange of substantially the same design carries a plurality of first electrodes 24, each provided with the corona discharge points 25, at equidistant angular intervals. The two flanges 21, together with the preferably bar-shaped electrodes 24, may form a stable structure resembling a cage provided with means (not shown) on the flanges for attaching the cage to a machine or plant to which the equipment is to be fitted. The bar-shaped first electrodes 24 function as spacing rods between the flanges 21.

Second electrodes 26 are equidistantly spaced between the first electrodes 24 at a radial distance from the axis of the equipment which is at most equal to that of the first electrodes. The first and the second electrodes shown in FIGS. 4 and 5 may be designed to exactly the same pattern as the electrodes 4 and 5 in FIGS. 1 and 2. During service, the electrodes 24 are connected to earth potential and, in the event of one or both flanges 21 being of metal, they are conveniently electrically connected in parallel by the metal flange(s). The electrodes 26 are insulated lengths of electrical conductor and, when the equipment is in service, they are electrically connected to the high voltage terminal of a high voltage source (not shown).

FIG. 4 is a schematic cross section on an enlarged scale showing the screw fastening of an electrode 24 to one of the flanges 21, whereas FIG. 5 is a cross section of the mode of connection of an electrode 26 to a flange 21, a bushing 27 being provided for the passage trically insulating material which is located in the bore of the flange. On the outside of the flange 21 this bushing 27 fits into the opening of a washer 28 which is also of electrically insulating material. A compression spring 29 bears against the face of the washer 28, and urges a spring retainer 30, (similar to spring retainer 8 already referred to in FIGS. 1 and 2), outwards for the purpose of keeping the conductor length forming the second electrodes 26 tensioned and thereby ensuring that the distance of the electrodes 26 from the neighbouring electrodes 24 and from the workpiece 23 will always remain the same.

The electrodes 26 are all identical and, as already mentioned with reference to FIGS. 1 and 2 they form parts of a continuous single conductor forming consectuive hairpins. Alternatively they may be separate conductor lengths having insulated surfaces in the regions in which they confront the electrodes 24 and may be connected together in series, one or both ends of the linked series of conductors being connected to the high voltage terminal of the high voltage source.

The equipment shown in FIGS. 3, 4 and 5 may be of any desired axial length, provided the problem of electrode stability can be satisfactorily solved. For ensuring parallelism between the several electrodes and equal distances from the workpiece, annular intermediate support means (not shown) may also be provided in this embodiment.

Further to illustrate the versatility of design of the proposed equipment, though by no means exhausting the available possibilities, FIG. 6 shows a partial sectional view of an embodiment which is suitable for treating tubular stock or materials that have been formed into an at least partly cylindrical form, and which may also function as a stationary or slowly moving deflecting device for a travelling web of material. Like FIG. 3, FIG. 6 is a cross sectional view, 41 being a section of the material being treated, 42 one of the bearing supports, which are here shown as annular flanges, and 43 and 44 being first and second electrodes of the same design and affixed in an analogous way as already described.

What is claimed is:

1. In a system for discharging an electrostatic potential from a surface of a material that is a poor conductor of electricity by passing the material through an electric corona discharge generated between at least one pair of electrodes extending between lateral bearing members, a first electrode of each pair of said at least one pair of electrodes being connected to ground, a second electrode of each pair of said at least one pair of electrodes being connected to a high potential voltage source, the improvement comprising:

each of said first electrodes comprising rigid conductor rods rigidly connected to at least one of said bearing members, each of said rigid conductor rods having spaced therealong discrete separate discharge points; and

each of said second electrodes comprising smoothsurfaced sections of a continuous electrical con ductor resiliently connected between said bearing members in a zig-zag fashion, each of said sections between said bearing members being completely covered with a coating of electrical insulation.

2. The improvement claimed in claim 1, wherein each of said second electrodes are located closer to said surface of said material than said first electrodes.

3. The improvement claimed in claim 1, wherein said bearing elements comprise end plates, each of said rigid conductor rods being rigidly fixed at opposite 5 ends thereof to said end plates, said rigid conductor rods and said end plates thus forming a self-supporting ing said second electrodes. 

1. In a system for discharging an electrostatic potential from a surface of a material that is a poor conductor of electricity by passing the material through an electric corona discharge generated between at least one pair of electrodes extending between lateral bearing members, a first electrode of each pair of said at least one pair of electrodes being connected to ground, a second electrode of each pair of said at least one pair of electrodes being connected to a high potential voltage source, the improvement comprising: each of said first electrodes comprising rigid conductor rods rigidly connected to at least one of said bearing members, each of said rigid conductor rods having spaced therealong discrete separate discharge points; and each of said second electrodes comprising smooth-surfaced sections of a continuous electrical conductor resiliently connected between said bearing members in a zig-zag fashion, each of said sections between said bearing members being completely covered with a coating of electrical insulation.
 2. The improvement claimed in claim 1, wherein each of said second electrodes are located closer to said surface of said material than said first electrodes.
 3. The improvement claimed in claim 1, wherein said bearing elements comprise end plates, each of said rigid conductor rods being rigidly fixed at opposite ends thereof to said end plates, said rigid conductor rods and said end plates thus forming a self-supporting body.
 4. The improvement claimed in claim 3, further comprising support means formed of electrical insulation material positoned between said end plates for supporting said second electrodes. 